© 2000 Heron Publishing—Victoria, Canada
Photosynthetic nitrogen-use efficiency in evergreen broad-leaved woody species coexisting in a warm-temperate forest
Kouki Hikosaka (1) and Tadaki Hirose (1)
1. Biological Institute, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578, Japan / Received February 10, 2000
Summary
Photosynthetic nitrogen-use efficiency (PNUE, photosynthetic capacity per unit leaf nitrogen) varies among species from different
habitats and correlates with several ecological characteristics such as leaf life span and leaf mass per area. We investigated
eight evergreen broad-leaved woody species with different leaf life spans that coexist in a warm-temperate forest. We determined
photosynthetic capacity at ambient CO2 concentration in saturated light, nitrogen concentration, and the concentration of ribulose-1,5-bisphosphate carboxylase
(RuBPCase), a key enzyme of photosynthesis and the largest sink of nitrogen in leaves. Each species showed a strong correlation
between photosynthetic capacity and RuBPCase concentration, and between RuBPCase concentration and nitrogen concentration.
Photosynthetic capacity of leaves decreased with increasing leaf life span, whereas PNUE did not correlate significantly with
leaf life span. There was a twofold variation in PNUE among species. This relatively small variation in PNUE is consistent
with the argument that species that coexist in a single habitat maintain a similar PNUE. The two components of PNUE—photosynthetic
rate per unit RuBPCase and RuBPCase per unit leaf nitrogen—were not significantly correlated with other leaf characteristics
such as leaf life span and leaf mass per area. We conclude that differences in PNUE are relatively small among coexisting
species and that differences in absolute amounts of photosynthetic proteins lead to differences in photosynthetic productivity
among species.
Keywords:
coexistence, leaf life span, leaf nitrogen, leaf photosynthesis, ribulose-1,5-bisphosphate carboxylase.
